Alternative To Dynamic SQL In A Function

Hi all, I have a sql problem i'd like to put to the masses because its driving me crazy! Before I start, this is a database i inherited so I cant change the schema.

I have a table which holds field information for a form, namely the table name, column name and some other irrelevant stuff (X/Y coordinates for printing onto a document). Here is some sample data to explain better:
TableName              FieldName                Xpos             Ypos
----------               ---------                -----            -----
FruitTable                FruitName                10                20
VegTable                 VegName                 10                40
FruitTable                FruitColour               20                10  
(Thats not the real data of course)
What I need is a calculated field which returns the value of each field from each table – probably by constructing a dynamic sql statement(?) It would look something like this:
Select @FieldName From @TableName Where bla bla bla â€“ don’t worry about the where clause. The completed dataset will hopefully then look like this:
TableName              FieldName                Xpos             Ypos             FieldValue (calculated field)
----------               ---------                -----            -----            ---------      
FruitTable                FruitName                10                20                Oranges (result of: Select FruitName From FruitTable Where....)
VegTable                 VegName                 10                40                Parsnips (result of: Select VegName From VegTable Where....)
FruitTable                FruitColour               20                10                Green (result of: Select FruitColour From FruitTable Where....)
 
I have tried creating a scalar-valued function which takes TableName and FieldName as parameters and creates a dynamic sql string, but i cannot seem to execute the sql once I have built it. Here is a general idea of how I was trying to use the function:
Main query:Select
TableName, FieldName, Xpos, Ypos,
dbo.GetFieldValue(TableName, FieldName) As FieldValue
From
tblFieldAndPosition---------------Function: CREATE FUNCTION GetFieldValue (@TableName nvarchar(255),@FieldName nvarchar(255))

RETURNS nvarchar(255)
AS
BEGIN

Declare @SQL nvarchar(max)
Set @SQL = 'Select ' + @FieldName + ' From ' + @TableName

sp_executesql @SQL??

return ???

END ------------------------- The alternative to getting this data all out at once is contructing the sql statement in code and going back to the database once for every row - which i really dont want to do. If anyone has had a situation like this before, or can point me in the right direction I will be very very grateful.  Hope thats clear. Thanks in advance